In the related art, various types of multistage compressors applicable to an air conditioning apparatus are proposed. As a known example, there is a multistage compressor for two-stage compression in which a low-stage side rotary compressing mechanism is provided under an electric motor provided at a center portion in a closed housing, and compressed gas is discharged into the closed housing and intermediate pressure gas is taken into a high-stage side scroll compressing mechanism provided above the electric motor (for example, see Patent Document 1).
There is also proposed in Patent Document 2 a multistage compressor for two-stage compression in which an electric motor and low-stage side and high-stage side rotary compressing mechanisms are provided in the closed housing, intermediate pressure gas compressed by the low-stage side rotary compressing mechanism is discharged to a second sealed chamber provided in the closed housing, the intermediate pressure gas extracted from the side of a refrigerant circuit is injected into the second sealed chamber, and the intermediate pressure injection gas and the intermediate pressure gas compressed by the low-stage side rotary compressing mechanism are taken into the high-stage side rotary compressing mechanism.
There is proposed in Patent Document 3 a multistage compressor for two-stage compression in which R410A refrigerant is used and intermediate pressure gas compressed by a low-stage side rotary compression element is taken into a high-stage side rotary compression element via a gas pipe and the intermediate pressure gas extracted from the side of the refrigerant circuit is injected into the gas pipe, and in which the ratios of displacement volume of the low-stage side compression element and the high-stage side compression element are 1:0.65 to 1:0.85.
In Patent Document 4, there is proposed a multistage compressor for two-stage compression in which part of CO2 refrigerant gas compressed by the low-stage side rotary compression element is discharged into the closed housing, and the intermediate pressure CO2 refrigerant gas and the remaining intermediate pressure CO2 refrigerant gas is taken into the high-stage side rotary compression element via the gas pipe, and in which the volumetric ratios of the low-stage side compression element and the high-stage side compression element are 1:0.56 to 1:0.8.
[Patent Document 1] JP-A-5-87074
[Patent Document 2] JP-A-2000-54975
[Patent Document 3] JP-A-2006-152839
[Patent Document 4] JP-A-2001-73976